1. Field of the Invention
This present invention relates to semiconductor substrate handling equipment, and in particular, to swapping front-opening unified pods (FOUP) within a processing tool during the tool run time.
2. Description of Related Art
Semiconductor wafers, or other such substrates, are typically subjected to many processing steps that involve moving a cassette of wafers from one type of apparatus to another. For example, wafers contained within a wafer-storage cassette may be moved individually to a processing chamber for depositing and patterning layers of material for forming integrated circuit chips.
During semiconductor manufacturing, it is essential that the processed wafers be kept isolated from contamination when being transferred. As such, robotic handling devices are often used since human handling is more likely to cause contamination. These robotic handling devices store and transfer the wafer-storage cassettes within a sealed box or pod. One such pod is known as a Front Opening Unified Pod (FOUP). Automated transfer systems have been designed for use with FOUPs for lifting and lowering the FOUPs by automated material handling systems (AMHS).
A FOUP protects wafers from contamination by moving the wafers within a sealed environment. In so doing, each FOUP includes a door with an opening portion and a load port for opening/closing the opening portion. The FOUP door faces the opening portion of the load port. When wafers are loaded into the FOUP, the door opens, wafers are robotically conveyed into the FOUP opening portion, and the door closes to enclose the wafers within the FOUP. Likewise, in unloading the FOUP, the door opens, wafers are robotically transferred from the FOUP opening portion, and the door closes to provide an empty FOUP.
The practice of swapping wafers from one FOUP to another, hereinafter referred to as “FOUP swapping”, is used in a number of different semiconductor fabrication processing techniques. For instance, FOUP swapping is used for contamination protection, whereby wafers are moved from a “dirty” FOUP into a “clean” FOUP. An external mapper/sorter tool is used to swap the wafers from the dirty FOUP into the clean FOUP. After the swap is complete, the wafers are conveyed to the next processing step within the clean FOUP, and the dirty FOUP is cleaned for reuse. FOUP swapping is also used for process segregation to keep specific types of wafers separated from other types of wafers, such as, from keeping non-copper wafers away from those wafers having copper processing levels. A number of different designated external mappers are often used for process segregation FOUP swaps.
Split and merge routing/recipe operations also involve FOUP swapping. A split occurs when a selected subset of wafers within a FOUP is required to follow an alternate process path as compared to other wafers within the FOUP. The wafers within the FOUP are robotically transferred to an external mapper, wherein the wafers are then split into different FOUPs for transferring the different subsets of wafers to different processing tools for carrying out the various semiconductor fabrication techniques. FOUP swapping is also used during FOUP maintenance techniques whereby wafers are removed from a FOUP in need of repair and transferred to another FOUP. FOUP maintenance also involves the use of an external mapper tool.
FIG. 1 shows a conventional FOUP swapping technique and process flow. A set of wafers is robotically transferred into a dirty FOUP 6 (step 10). FOUP 6 is referred to herein as the “dirty FOUP” since it receives and carries unprocessed wafers from an unclean environment, and/or it may have been exposed to contaminants residing on the unprocessed wafers themselves. The set of wafers are transferred into a processing tool 2 via FOUP 6, and unloaded into a chamber of this processing tool 2 (step 12). Upon wafer processing completion, the processed wafers are transferred from the processing tool back into the dirty FOUP 6 for transport to a mapper/sorter tool 4 (step 13). Undesirably, this step leads to the contamination and/or re-contamination of the processed wafers.
Also robotically transferred and sealed to the mapper tool 4 is an empty clean FOUP 8 (step 14). The FOUP 8 is referred to herein as the “clean FOUP” since it does not receive unprocessed wafers from a potentially unclean environment for transferring such wafers to a processing tool. Once the dirty FOUP 6 is sealed to the mapper tool 4, the processed wafers are unloaded from the dirty FOUP 6 into the mapper tool 4 (step 15), and the empty, dirty FOUP 6 is sent for cleaning (step 16). The mapper tool 4 transfers the processed wafers into the clean FOUP 8 (step 17), and these wafers are then carried to the next semiconductor fabrication process within FOUP 8 (step 18).
However, since the processed wafers may have been contaminated once transferred back into the dirty FOUP 6 in step 13, these contaminated processed wafers may also be transferred into the mapper tool, into the clean FOUP 8 and may deleteriously affect further processing techniques. Inventions that can improve FOUP swapping techniques are highly desirable since the current techniques are costly, at increased risk of wafer contamination, require numerous processing steps, time consuming, require increased AMHS traffic, and are inefficient.